1. Field of the Invention
The present invention relates generally to well abandonment tools for cutting and pulling casing and more particularly to casing retrieval systems for performing various functions in a single trip.
2. Description of the Prior Art
When it was required to cut the casing string in deep water from a semi-submersible rig, or to cut the casing string below 1,000 feet on a platform or jackup rig, the normal procedure was to cut the casing string with a conventional hydraulic pipe cutter. If the operator wanted to establish circulation, the rig's hydraulic blowout preventer was closed on the work string-casing annulus and pump pressure was applied to the work string. This procedure created a problem because the operation tended to damage the rig's blowout preventer and, as a result, was not considered a good operational procedure.
Heretofore, most operators preferred to pull the cutting tool from the wellbore and then use a casing spear and packoff. In this procedure, after the spear was set, pressure was applied to the workstring and circulation was attempted. There are several reasons for establishing circulation around the cut piece of pipe. The first reason is to ensure that there is no build up of gas bubbles. The second reason is to ensure that the pipe is cut and in condition to be retrieved, i.e. free of drilling fluid sediments or sand. Circulation would not go downwardly due to cement or packers sealing the lower annular area. If circulation was not established, the spear and packoff was removed from the wellbore and the cutter assembly was then re-run at a point higher in the hole. After the cut was made, the spear and packoff was re-run and another circulation attemp was made. Quite often this cumbersome procedure had to be repeated many times until circulation was established.
Another system utilized by Assignee was an assembly comprising a spear, a stabilizer and a hydraulic cutter. In this system, the casing was cut under tension and then pulled to ascertain whether the casing was free before the casing cutter was retrieved from the well bore.
The problem with this system was that it was not possible to pressure up on the cut, establish circulation and ascertain if there was a gas bubble or other problems behind the cut casing without using surface blowout preventers. As stated previously, operators were reluctant to do this.